The present invention generally relates to measurement of the distance of a shaft from the bottom of a vessel and the amount by which the shaft is offset from the center of the vessel. More particularly, the present invention relates to the precise measurement of shaft height and shaft offset in vessels employed in dissolution testing systems.
In the pharmaceutical industry, dissolution testing and analysis is required to be performed on samples taken from batches of tablets or capsules manufactured by pharmaceutical companies in order to assess efficacy and other properties. Dissolution analysis by automated means has become popular for increasing throughput and improving accuracy, precision, reliability, and reproducibility. Automation also relieves the tedium of manually performing a variety of requisite procedures, including: handling and delivering dosage units such as capsules and tablets; monitoring dissolution system parameters; manipulating the shafts carrying the agitation paddles or sample baskets; recording, displaying and printing accumulated data and test results; and cleaning and filtering the vessels employed in such procedures.
Despite the benefits accruing from automation, validation of the procedures employed in dissolution testing and analysis remains a critical consideration. A typical dissolution test requires, among other things, that a rotatable shaft equipped with a paddle or basket be properly positioned in the center of, and properly located a specified distance from the bottom of, a dissolution test vessel prior to conducting the test. The USP has promulgated guidelines for the pharmaceutical industry which are enforced by the FDA. Under USP 24, General Chapters, Dissolution (711), the shaft must be positioned such that its centerline is not more than 2 mm at any point from the vertical axis of the vessel, and such that the paddle or basket (typically mounted to the lower end of the shaft) be positioned at 25 mm xc2x12 mm from the bottom of the vessel.
Various hand-held devices have been utilized to carry out the measurements required to determine whether a shaft is positioned in a dissolution test vessel in compliance with the above-cited guidelines. Rulers, machinist calipers and micrometers, and pass/fail fixtures typify such devices and are known to persons skilled in the art. It is readily apparent to such skilled persons that operation of these devices requires a great deal of manual handling, with critical specifications largely determined by sight and feel. Conventional shaft measurement devices therefore engender an unacceptably high risk of error. There accordingly exists a long felt need for improved apparatus and methods for determining the position of a shaft installed in the vessel of a dissolution testing station.
In accordance with the present invention, an apparatus is mountable to a shaft disposed within a vessel and is adapted for measuring the magnitude by which the centerline of the shaft is offset from the central axis of the vessel. The apparatus comprises a housing and a plunger slidably mounted to the housing. The plunger has an outer section extending radially outwardly beyond a wall of the housing, and means such as a spring for biasing the plunger radially outwardly. A transducer is operatively mounted to the housing. The transducer is adapted to encode positions of the plunger and to produce an electrical signal proportional to a change in position resulting from displacement of the plunger. Means such as data lines are provided for transferring the signal to means such as a microprocessor for interpreting the signal.
In another embodiment according to the present invention, an apparatus is mountable to a shaft having a paddle or basket disposed within a vessel. The vessel has a central axis and a hemispherical end region. The apparatus is adapted for measuring the distance from a distal surface of the paddle or basket to a lowermost point on the inside surface of the hemispherical end region. The apparatus comprises a housing and a plunger slidably mounted to the housing. The plunger has an outer section extending outwardly beyond a wall of the housing, and means such as a spring for biasing the plunger outwardly. An end portion extends transversely from the plunger beneath the housing and is substantially centered about a central portion of the housing. A transducer is operatively mounted to the housing. The transducer is adapted to encode positions of the plunger and to produce an electrical signal proportional to a change in position resulting from displacement of the plunger. Means such as data lines are provided for transferring the signal to means such as a microprocessor for interpreting the signal.
In another embodiment according to the present invention, a system is provided for determining the location of a rotatable shaft in relation to a vessel mounted to a rack of a dissolution testing station. The shaft has a first end mounted to the testing station above the vessel, a second end disposed within the vessel and an operative component secured to the second end. The system comprises a housing including means such as a resilient clip and groove for removably mounting the housing to the shaft, and a plunger slidably mounted to the housing. The plunger has an outer section extending radially outwardly beyond a wall of the housing and extendable to an inside lateral surface of the vessel, and has means such as a spring for biasing the plunger radially outwardly. A transducer is operatively mounted to the housing. The transducer is adapted to encode positions of the plunger, and to produce an electrical signal proportional to a distance from a reference position to an extended position at which the plunger is in contact with the inside lateral surface of the vessel. Means such as data lines are provided for transferring the signal to means such as a microprocessor for interpreting the signal.
In another embodiment according to the present invention, a system is provided for determining the location of a rotatable shaft in relation to a vessel. The vessel has a central axis and a hemispherical end region, and is mounted to a rack of a dissolution testing station. The shaft has a first end mounted to the testing station above the vessel, a second end disposed within the vessel and an operative component such as a paddle or basket secured to the second end. The system comprises a spherical object removably disposed in a lowermost point on an inside surface of the hemispherical end region of the vessel. A housing includes means such as a resilient clip or groove for removably mounting the housing to the shaft. A plunger is slidably mounted to the housing. The plunger has an outer section extending beyond a wall of the housing and extendable to the spherical object, and has means such as a spring for biasing the plunger outwardly. An end portion has an upper surface and a lower surface, and extends transversely from the plunger and between the operative component and the spherical object.
A transducer is operatively mounted to the housing. The transducer is adapted to encode positions of the plunger, and to produce an electrical signal proportional to a distance from a reference position at which the top surface of the end portion of the plunger is biased against the operative component to an extended position at which the lower surface is in contact with the spherical object. Means such as data lines are provided for transferring the signal to means such as a microprocessor for interpreting the signal.
In another object according to the present invention, a system is provided for determining the location of a shaft in relation to a vessel in which the shaft is disposed. The vessel has a central axis and a hemispherical end region. The system comprises a shaft offset measurement device which includes a first housing and a first plunger slidably mounted to the first housing. The first plunger has an outer section extending radially outwardly beyond a wall of the first housing and means such as a spring for biasing the first plunger radially outwardly. A first transducer is operatively mounted to the first housing. The first transducer is adapted to encode positions of the first plunger and to produce a first electrical signal proportional to a change in position resulting from displacement of the first plunger.
The system further comprises a shaft height measurement device which includes a second housing and a second plunger slidably mounted to the second housing. The second plunger has an outer section extending outwardly beyond a wall of the second housing, and means such as a spring for biasing the second plunger outwardly. An end portion extends transversely from the second plunger beneath the second housing and is substantially centered about a central portion of the second housing. A second transducer is operatively mounted to the second housing. The second transducer is adapted to encode positions of the second plunger and to produce a second electrical signal proportional to a change in position resulting from displacement of the second plunger.
The system further comprises a console including logic means such as a microprocessor for effecting interpretations of the first and second electrical signals and means such as an LCD display for displaying the interpretations in human-readable form. Means such as data lines are provided for transferring the first and second electrical signals to the logic means.
In another embodiment according to the present invention, an apparatus is adapted for measuring the magnitude by which the centerline of a shaft is offset from the central axis of a vessel in which the shaft is disposed, and for measuring the distance from a distal end of the shaft to the lowermost point on an inside surface of a hemispherical end region of the vessel. The apparatus comprises a mounting assembly, a lateral plunger slidably mounted to the mounting assembly, a lateral transducer operatively disposed with respect to the mounting assembly and to the lateral plunger, a vertical plunger slidably mounted to the mounting assembly, and a vertical transducer operatively disposed with respect to the mounting assembly and to the vertical plunger.
The lateral plunger has means such as a spring for biasing the lateral plunger radially outwardly. The lateral transducer is adapted to encode positions of the lateral plunger and to produce an electrical signal proportional to a change in position resulting from displacement of the lateral plunger. The vertical plunger has means such as a spring for biasing the vertical plunger downwardly with respect to the mounting assembly, and includes an upper end portion extending transversely from the vertical plunger. The vertical transducer is adapted to encode positions of the vertical plunger and to produce an electrical signal proportional to a change in position resulting from displacement of the vertical plunger. Means such as data lines are provided for transferring the signals produced respectively by the lateral and vertical transducers to means for interpreting the signals. The signal interpreting means can include a console with which the signal transferring means communicates, wherein the console has logic means such as a microprocessor for effecting interpretations of the signals and means such as an LCD display for displaying the interpretations in human-readable form.
The present invention also provides methods for determining the position of a shaft installed in a vessel with respect to the central axis of the vessel and/or lowermost point inside the vessel.
Accordingly, a method is provided for measuring the amount by which the centerline of a shaft is offset from the central axis of a vessel in which the shaft is to be disposed, comprising the following steps. A measurement device which includes a radially outwardly biased plunger is mounted to the shaft. The plunger has a settable zero reference position. The shaft is inserted into the vessel at a normal operating position of the shaft, wherein a distal end of the plunger is in contact with a lateral inside surface of the vessel at a first distal plunger position. A first displaced plunger position is defined as a position on the plunger located a distance by which the plunger has moved in relation to the zero reference position, the distance being equal a first displacement magnitude.
The displacement magnitudes are measured by encoding the displaced plunger position and interpreting the displaced plunger position in relation to the zero reference position, wherein the displacement magnitudes determine the shaft centerline offset amount. A value for the shaft centerline offset amount is calculated based on the measured first displacement magnitudes. Finally, a signal is produced which is indicative of the shaft centerline offset amount.
Accordingly, another method is provided wherein a distal end of the plunger position is in contact with a lateral inside surface of the vessel at a first distal plunger position. This first displaced plunger position is reset to the zero reference position. The shaft is then rotated one full revolution while continuously sampling the displacement of the plunger position is defined as a position on the plunger located a distance by which the plunger has moved in relation to the zero reference position, the distance being equal to the displacement magnitude from this continuous sampling, the lowest and the largest displacement magnitudes are kept.
Another method according to the present invention is for measuring a shaft height, which is defined as the distance between the distal end of a shaft and the inside lowermost surface of a hemispherical end region of a vessel in which the shaft is to be disposed. The method comprises the following steps. A measurement device which includes a downwardly biased plunger is mounted to the shaft. The plunger includes an end portion. The end portion extends below the shaft and has a predetermined end portion height. A zero reference position of the plunger is defined by urging the end portion against the distal end of the shaft. The zero reference position is encoded. The inside lowermost surface of the hemispherical end region of the vessel is located by inserting a spherical object having a predetermined diameter into the vessel. The shaft is inserted into the vessel at a normal operating position of the shaft, permitting the end portion of the plunger to contact the spherical object.
A displaced plunger position is defined as a position on the plunger located a distance by which the plunger has moved in relation to the zero reference position in order to contact the spherical object, the distance being equal to a displacement magnitude. The displacement magnitude is measured by encoding the displaced plunger position and interpreting the displaced plunger position in relation to the zero reference position, wherein the sum of a predetermined constant plus the displacement magnitude is proportional to the shaft height. A value for the shaft height is calculated based on the measured displacement magnitude. A signal is produced which is indicative of the shaft height.
A further method according to the present invention is for measuring the amount by which the centerline of a shaft is offset from the central axis of a vessel in which the shaft is to be disposed, and for measuring a shaft height defined as the distance between the distal end of the shaft and the inside lowermost surface of a hemispherical end region of the vessel. The method comprises the following steps. The inside lowermost surface of the hemispherical end region of the vessel is located by inserting a spherical object into the vessel. A measurement device is mounted over the vessel. The measurement device includes a lateral plunger and a vertical plunger. The vertical plunger includes an end portion. The shaft is inserted into the vessel at a normal operating position of the shaft.
A distal end of the lateral plunger is permitted to contact a lateral inside surface of the vessel. A displaced lateral plunger position is defined as a position on the lateral plunger located a lateral distance by which the lateral plunger has moved in relation to a predetermined zero reference position of the lateral plunger, the lateral distance being equal to a lateral displacement magnitude. The lateral displacement magnitude is measured by encoding the displaced lateral plunger position and interpreting the displaced lateral plunger position in relation to the zero reference position of the lateral plunger, wherein the lateral displacement magnitude determines the shaft centerline offset amount. A value for the shaft centerline offset amount is calculated based on the measured lateral displacement magnitude. A signal is produced which is indicative of the shaft centerline offset amount.
The end portion of the vertical plunger is permitted to contact the spherical object. A displaced vertical plunger position is defined as a position on the vertical plunger located a vertical distance by which the vertical plunger has moved in relation to a predetermined zero reference position of the plunger, the vertical distance being equal to a vertical displacement magnitude. The vertical displacement magnitude is measured by encoding the displaced vertical plunger position and interpreting the displaced vertical plunger position in relation to the zero reference position of the vertical plunger, wherein the vertical displacement magnitude determines the shaft height. A value for the shaft height is calculated based on the measured vertical displacement magnitude. A signal is produced which is indicative of the shaft height.
It is therefore an object of the present invention to provide an apparatus for measuring the amount by which the centerline of a shaft disposed in a vessel is offset from the central vertical axis of the vessel.
It is another object of the present invention to provide an apparatus for measuring the height of such shaft above the lowermost inside point of the vessel.
It is a further object of the present invention to provide an apparatus for controlling the process by which the shaft centerline offset amount and shaft height are measured, and for expressing the results of such process using peripheral devices.
It is yet another object of the present invention to provide improved methods for determining accurate values for the shaft centerline offset amount and shaft height.